A photoresist pattern forming process, i.e., one of semiconductor device manufacturing processes, forms a thin resist film on a surface of a semiconductor wafer (hereinafter, referred to simply as “wafer”), exposes the resist film to transfer a predetermined circuit pattern to the resist film and develops the circuit pattern by processing the exposed resist film with a developer, namely, a processing liquid, to form a mask pattern on the surface of the wafer. Usually, these processes are carried out by a system built by connecting an exposure system to a coating and developing system that forms a resist film and develops the exposed resist film.
A known developing process is carried out in the following manner. For example, as shown in FIG. 14(a), a wafer W is held in a horizontal position on a spin chuck 1 capable of rotating about a vertical axis. A developer D is discharged onto the surface of the wafer W through, for example, a developer nozzle 11 provided with a straight discharge opening of a length equal to the diameter of the wafer W while the developer nozzle 11 is moved in a horizontal plane extending slightly above the surface of the wafer 11 to develop the wafer W. Subsequently, as shown n FIG. 14(b), the wafer W is rotated about a vertical axis and a rinsing liquid R, such as pure water, is poured onto a central part of the surface of the wafer W through an upper rinsing nozzle 12 and onto a peripheral part of the back surface of the wafer W through a lower rinsing nozzle 13. The rinsing liquid R is forced to spread over the entire surface of the wafer W and the entire peripheral part of the back surface of the wafer W by centrifugal force acting on the rinsing liquid R while the wafer W is rotating to clean the wafer W. Then, as shown in FIG. 14(c), the wafer W is rotated at a high rotating speed to dry the wafer W by spin drying that shakes the rinsing liquid R off the wafer W.
When the developer D is poured onto the surface of the wafer W, the surface tension of the developer D spreads the developer D through the circumferential surface of the wafer W to the back surface in some cases. A large cleaning mechanism is needed to remove the developer D spread radially inward on the back surface. A known liquid seal forming method forms a liquid film (liquid seal) on a peripheral part of the back surface of a wafer W to restrain the developer D from flowing through the circumferential side surface of the wafer W to the back surface. (Such liquid seal forming methods are disclosed in, for example, Patent documents 1 and 2.) The liquid seal forming method will be briefly described with reference to FIG. 15. A cylindrical wall 14 is space from the back surface of a wafer W by a small space. An annular groove or the like is formed in the upper end surface of the cylindrical wall 14. For example, the wafer W is rotated about a vertical axis and, for example, pure water is discharged in to the space between the back surface of the wafer W and the upper end surface of the cylindrical wall 14 through a lower rinsing nozzle 13 before a developer D is discharged onto the surface of the wafer W. Pure water is retained by surface tension in the entire space in a liquid seal 15 to restrain the developer D from flowing to the back surface of the wafer W.
Patent document 1: Specification of Jpn. Pat. No. 2903284 (Second embodiment, FIGS. 11 and 12)
Patent document 2: Specification of Jpn. Pat. No. 3198377 (Paragraph 0054, FIG. 1)